It's always been Fat Tuesdays in the past but that's gone now. I don't think any of the other clubs do the Mardi Gras thing on a regular basis.
Oops, forgot about them...I always think of them more aligned to St Patrick's day but you're right...they do Mardis Gras as well.
last year the Mardi Gras party was held at Margarittaville, which was very awsome, but now that Pat O's is back up and running, I would imagine it will be there!